The field of the invention is motor protection circuits for minimizing motor damage due to overheating, ground faults or bearing failure.
There are numerous commercially available circuits and devices for detecting potentially damaging conditions for motors employed in industrial applications. These include, for example, circuits for detecting phase imbalances as disclosed in U.S. Pat. No. 3,736,470; circuits for detecting ground fault conditions as disclosed in U.S. Pat. No. 3,968,409; and overload relays such as that disclosed in U.S. Pat. No. 4,157,523. In large motor controls such as that disclosed in U.S. Pat. No. 3,896,353, such circuits and devices, operate to shut down the motor when potentially damaging conditions are sensed. Such motor protection systems are often custom built for each application, and once delivered, the user has limited ability to alter the conditions, or operating parameters, which will shut the motor down.
Although programmable devices have become available which enable the user to preset the trip levels of various operating parameters, such devices are costly and have limited diagnostic capabilities.